The manufacture of semiconductor integrated circuits has become a competitive, high volume commodity business. As such, controlling the cost of each completed circuit improves the commercial effectiveness of that circuit. For the semiconductor manufacturing industry, the time necessary to complete each manufacturing step has a direct relationship and effect on the cost of that circuit. One time-consuming phase during the fabrication of semiconductor devices is singulation. Singulation is a process for dicing a sheet of fabricated semiconductor die and/or packages into individual units. Semiconductor dice are typically mass produced on a wafer and good dice are mounted on a leadframe. The leadframes are also typically mass produced in large batches by the sheet. Depending on the manufacturing process, the sheet of leadframes can have an adhesive (dicing) tape applied to one side of the sheet before an encapsulation is applied to the dice mounted on the leadframes. The encapsulation is typically performed by molding a plastic resin to the sheet of dice and leadframes. In these cases, the dicing tape provides a lower support structure for the formation of the plastic molding during encapsulation. The encapsulation is commonly referred to as a semiconductor package.
A singulation process separates each package from the molded sheet. The molded sheet is typically divided into molded strips for singulation. There are various techniques currently being practiced for singulation. One technique involves punching, while another technique involves sawing the molded strip to separate the packages from the molded strip. Two particular drawbacks related to sawing the molded strip are (1) lengthy singulation times and (2) defects in the singulated product. Both drawbacks are related to the heat generated by the singulation blade. The saw blade cuts the resin and can cut the lead frame into a plurality of particles. While cutting, the blade forms a well-known trench-like kerf. The kerf can fill with particles which can bind between the blade and a wall of the kerf. The particles can damage the wall of the kerf leading to failures or reliability problems.
In a conventional process, the singulation blade is generally operated at a rotational (spindle) speed of 20,000 rotations per minute (RPM), and a table speed of two inches per second (IPS). These speeds are typical of a conventional “Disco” type singulation machine. As is commonly understood in the art, the table speed measures the (linear) speed of the blade moving along a molded strip during singulation of the molded strip, whereas the spindle speed approximates the rotational speed of the blade (about its axis), as the blade cuts through the molded strip.
The relatively slow conventional speeds are used in the art to reduce blade overheating, to preserve blade life, and to reduce the number of defects in the singulated product. As mentioned above, speeding up the singulation process is beneficial to improve throughput and thereby reduce costs associated with semiconductor manufacturing. While increasing the rotational speed of the blade can promote faster singulation, there are significant tradeoffs in a conventional singulation process. Higher blade speeds increase blade temperature, which results in lower cutting efficiency, higher blade wear, and more singulation defects.
To cool the blade, certain conventional singulation processes use deionized (DI) water. However, simple deionized water does not operate adequately to (1) cool the blade, (2) lubricate the blade, and (3) remove the buildup of particles on and around the blade and in the kerf during singulation, and particularly at higher RPM and/or lateral (IPS) blade movement. Simple deionized water has certain properties that inhibit proper service as a lubricant and coolant. One such property is the high surface tension of water, which causes the water to form high tension beads. The high tension beads do not distribute well over large surface areas, and do not penetrate into small spaces such as the kerf. Hence, the high tension beads do not adequately cool and lubricate high speed singulation blades, and do not properly remove the buildup of particles, which obstruct the blade during singulation. These obstructions lead to higher friction between the blade and the kerf, and the higher friction further causes high power consumption by the electric motor and other components of the blade. Thus, there is a need to accelerate the singulation process without negatively affecting the quality or reliability of the singulated product, or the longevity of useful blade life.